A certain number of devices that allow a bezel to be replaced by another for aesthetic or functional reasons, particularly in a wristwatch, are already known. For an aesthetic purpose, this for example allows the colour of the most visible part of the watch to be match with that of clothing, at little cost. For a functional purpose, the replacement of the bezel for example allows the indications carried by said bezel to be altered, or the movement to be acted upon in order to have a multi-function watch. EP Patent No. 0 603 353 discloses a watch wherein replacement of the bezel allows the current time display to pass to a “football” or “tennis” mode, the selected bezel then comprising indications relating to such sports and means for controlling the watch mechanism in accordance with the rules of said sports.
According to the known prior art, a removable bezel is set in place and held, or conversely replaced, using devices that can be classified in two large categories, if inconvenient devices, requiring for example screwing, are excluded.
A removable bezel can be fixed by resilient means, as is disclosed in GB Patent No. 286 107. These resilient means can be formed by an elastomeric ring of suitable shape as disclosed in Japanese Utility Model No 4134/78. It may also be a snap fit device as is disclosed in U.S. Pat. No. 5,005,161. In all these resilient assemblies it is difficult to find a good compromise between a device that is sufficiently flexible to allow a user to replace the bezel without any particular effort and a device that is sufficiently secure to prevent it being accidentally lost.
In order to overcome the aforementioned drawback, a certain number of designs propose fixing the bezel to the middle part by means of a so-called “bayonet” device. The device consists in providing in the bezel and in the top part of the middle part or back cover-middle part, complementary male and female means that engage in each other when a movement of rotation is imparted to the bezel. A security system for locking/unlocking the bezel is also generally provided. A design of this type is disclosed in U.S. Pat. No. 5,490,123, the security system being formed by a push-button located on a horn of the case. In EP Patent Application No. 1 249 741, the bayonet device comprises a locking system formed of sinks arranged in the middle part and housing a spring for pushing a ball into recesses made in the inner face of the bezel. These constructions also have the drawback of being relatively complex and having a certain fragility, particularly when the bayonet device is set in place with a rotational movement of the bezel that is too forced and capable of damaging the assembling elements.